Various processes have been known and utilized in the prior art for the separation of air into its nitrogen and oxygen dominant constituents. Additionally, the use of a single pressure distillation column is known to have been used in the prior art for such separations.
In U.S. Pat. No. 3,214,926 a method for producing liquid oxygen or liquid nitrogen is set forth. However, in the patent it is necessary to have two distillation columns, one at high pressure and another at low pressure in order to extract liquid oxygen. No teaching is set forth in the text of the patent in which compression is provided by the energy derived from the separation streams.
In U.S. Pat. No. 3,217,502 a system is described which utilizes a single pressure distillation column. The product of this air separation system is liquid nitrogen. Oxygen which is separated out in this system is vented to waste. In this patent, it is the oxygen waste stream which is expanded in order to provide refrigeration for the air separation system. Power recovery from the waste stream is not set forth.
An air separation unit for the production of oxygen is disclosed in U.S. Pat. No. 3,394,555 wherein the combustion of a separate fuel source such as powdered coal is burned with oxygen or an air-oxygen mixture in which the oxygen is derived from the air separation unit. This combustion process provides power for the compression of helium gas for refrigeration necessary to the cryogenic separation system. Power from such combustion is derived from a magnetohydrodynamic power generator. Only a single feed to the single stage distillation column is contemplated in this patent.
U.S. Pat. No. 3,731,495 discloses an air separation system using an air feed compressor which is powered by combustion gases directed through a turbine. The turbine exhaust heats boiler steam to supplement the compressor drive. Electric generation is also considered. However, this reference does not utilize split feeds to the distillation column and in fact utilizes two separate columns at separate pressures for the recovery of the individual gaseous components of air which are separated.
U.S. Pat. No. 4,152,130 discloses an air separation unit which has multiple feeds to a two pressure-two stage distillation column. Both feeds to the distillation column are expanded through an expander. The system may produce liquid oxygen or liquid nitrogen as desired. The recovery of power from a waste stream from the air separation unit is not contemplated.
Low purity oxygen is produced in an air separation unit described in U.S. Pat. No. 4,254,629. Split feeds of the air to be separated are contemplated by the patent, but the use of at least two columns at high and low pressure are necessary. The recovery of power by combustion from a waste stream from the separation unit is not taught.
The art as represented above has failed to disclose an efficient manner in which to separate oxygen from air with the utilization of the by-products or waste streams in order to recycle energy necessary for compression both of the feed air and the oxygen product. In addition, the prior art has failed to minimize capital expenditures in separating air by the utilization of a single pressure distillation column. The solution to problems such as these are the objectives of the present invention.